Two parallel lines are intersected by a transversal. If one of the interior angles is 57°, what is the measure of its co-interior angle?
Answer: C
Co-interior angles (or consecutive interior angles) are on the same side of the transversal and between the parallel lines. They are supplementary, meaning their sum is 180°.
Let the other co-interior angle be x.
x + 57° = 180°
x = 180° - 57° = 123°.